Photographic emulsion containing supersensitized carbocyanines



March 30, 1937. c. E. K. MEES 2,075,048

PHOTOGRPHIC EMULSION CONTAINING SUPERSENSITIZED CARBOCYANINES OriginalFiled Nov. 4, 1952 ZOO 440 480 520 560 600 640 680 720 '760.

Ghaz'lesEfMee,

Empf/F U. 951;

Patented Mar. 3G, 1937 NITED -s'rATlifsl PHOTOGRAPHIC EMULSION CONTAININSUPERSENSITIZED CARBOCYANINES Charles E. K. Mees; Rochester, N.' Y.,assignor, by mesne assignments, to Eastman Kodak Company, Jersey City,N. J., a corporation of New Jersey Application November 4, 1932, SerialNo. 641,179 Renewed February 9, 1935 12 Claims.

This invention relates to sensitized photographic emulsions and moreparticularly relates to photographic emulsions such as those of thegelatino--silver-halide type containing a combination of sensitizers,one of which cooperates with the other to sensitize the emulsion to amuch greater degree than is possible with that sensitizer, or eithersensitizer alone, or eve`n than would be evidenced by the sum total ofthe sensil0 tization produced by the twoseparate sensitizersindividually.

In other Words, I have found that the sensitivity contributed tophotographic emulsions by certain sensitizers may be enhanced to a very15 considerable degree by adding to the basic sensitizer what I willterm a supersensitizer, the latter contributing to the emulsion thesensitivity which is peculiar to itself as well as activating orinducing further sensitivity in what I will term the basic sensitizer.For example, a certain basic sensitizer may have a green speed of 50 Hand D but when there is added thereto a supersensitizer, which may noteven sensitize to the green at all (but to some other portion of thespectrum) the green speed of the basic sensitizer will be increased farbeyond its original green speed. Or, assuming the basic sensitizer tosensitize the emulsion to a green speed of 50 and the supersensitizer toseparately sensitize the emulsion to a green speed of 5, the addition ofthe supersensitizer to the basic sensitizer will sensitize the emulsionto a green speed beyond the sum total of the two separate green speeds,

namely to a green speed, for instance of 80.

The combinations of sensitizers and supersensitizers which are thesubject of the instant invention have the peculiar property that, inorder for the supersensitizer to increase the sensitivity of the basicsensitizer, the region of sen- 40 sitivity of the supersensitizer mustcoincide at least in part With the region of sensitivity of the basicsensitizer. The unusual effects obtained by the combinations ofsensitizers which constitute the instant invention result, therefore, 40from the unusual influence or relation Whichthe supersensitizers haveupon orl to the `respective basic sensitizers.

Accordingly, it is among the objects of 'my invention to provide aphotographic emulsion 50 which contains a basic sensitizer for theemulsion and which also contains a supersensitizer which contributes itsown individual sensitization to the emulsion and also increases thesensitization caused by the basic sensitizer. It is a further object ofmy invention to provide certain combinations or mixtures of sensitizersin a photographic emulsion which will contribute to the emulsion asensitivity (ability to respond to light) not heretofore obtainable witheither of 10 the individual sensitizers in the combination.

Other objects will become apparent to those skilled in the art upon afurther perusal of this specification.

I have found, for instance, that the sensitivity which thethiocarbocyanines contributeto a gelatino-silver-halide emulsion will bemarkedly increased if there is present in the photographic emulsionalong with each part of the thiocarbocyanine, from approximately 1% partor even less to approximately one part or even more of a 2:2 dialkyl 8alkyl dibenzothiocarbocyanine salt as a supersensitizer. I find thissupersensitizing effect upon the sensitizing properties of thethiocarbocyanines to be general withor representative of the 2:2 dialkyl8 alkyl dibenzothiocarbocyanine salts which themselves 'have the abilityof separately sensitizing photographic emulsions. The best resultsareobtained, however, where the thiocarbocyanine used as the basicsensitizer is substituted in the central position of the trimethenylchain by an alkyl group.

vReferring to the attached drawing, forming a part hereof, there isrepresented a hypothetical wedge spectrogramy illustrating my invention.The curve A shows the approximate sensitivity conferred upon lagelatino-silver-halide emulsion.

by a 2:2' dialkyl 8 alkyl thiocarbocyanine salt as a basic sensitizer.The curve B illustrates diagrammatically the sensitivity separatelyconterred upon the same gelatinosilver-halide emulsion by a 2:2' dialkyl8 alkyl dibenzothiocarbocyanine salt'. The curve C, however, illustratesthe sensitivity of the same photographic emulsion containing a smallpercentage of a solution in which is dissolved approximately equal partsof these two salts. v From this it will be apparent that the combinationor mixture of these sensitizers contributes to the photographic emulsiona sensitivity far beyond that which it is possible to obtain even fromthe sum total of the sensitization resulting from the individualsensitizers.

More specically my invention is accomplished by dissolving thesensitizing dyes in, for instance, methyl alcohol. The sensitizer andsupersensitizer are added to the alcohol, for instance, in equalproportions, although I have found that less than an equal amount of thesupersensitizer is normally sufficient to confer" upon the sensitizer anincreased sensitivity. For example, while I may dissolve in the methyl'alcohol solvent one part of the 2:2' dialkyl 8 alkyl thiocarbocyaninesalt, I may then add to the alcohol from 136 part or even less to onepart or even more of the 2:2' dialkyl 8 alkyl dibenzothiocarbocyaninesalt, depending upon the effect that is desired in the photographicemulsion. The exact ratio of the supersensitizer to the sensitizer isnot particularly important inasmuch as those skilled in the art lcanreadily determine by what ratio the greatest degree oi sensitization ofthe basic sensitizer can be obtained.

This solution of the sensitizer and. supersensitizer is then dilutedwith water and a volume containing from a few milligrams to as much as100 milligrams, and preferably from about 10 to 30 milligrams of thesensitizers, is then added'to 1000 ce. of a gelatino-silver-halideemulsion, such as is customarily employed in the art. Obviously, if thebasic sensitizer is greatly supersensitized by the supersensitizer, lessof the sensitizer combination will be necessary to obtain the desireddegree of sensitization in the emulsion. The emulsion may then be coatedupon a transparent support as is Well known in the art, either glass, ora. cellulose nitrate or acetate, or other cellulose derivative, basebeing satisfactory as the support.

As further illustrating my invention, I have tabulated hereinaftertypical examples of dibenzothiocarbocyanines which themselves have thepower of sensitizing a photographic emulsion nine iodide. 2:2 dimethyl5:5:8 triethyl thiocarand also have the ability of supersensitizing thesensitizing effect of the carbocyanines on the photographic emulsion.Compounds which are characteristic of those which I may employ assupersensitizers for the carbocyanines opposite which they are set, areas follows- Basic sensitizer Supersensitizer e io de. n 2:2 diethyl 8methyl thiocai'bocya- 2:2 dimethyl 8 ethyl 3:4:3'z4'dibenzothiocarbocyanine iodide.

2:2-diethyl 8 methyl thiocarbocye- 2:2' diethyl 8 methyl 3:4:324'

digenzothiocarbocyanine io- 2:2' dimethyl 8 ethyl 3:4:3'14

gigenzothiocarbocyanne iobocyanine iodide. 2:2'5:5 :8 pentaethylthiocarbocyanine iodide. 2:2 din 1etl 1yl8 ethyl thiocerbocyanineiodide. l

Other examples'showing the broad application of my invention could becited, although the foregoing will be sufficient to teach those skilledin the art the manner in which my invention is carried out and the broadprinciple of supersensitizing basic sensitizers of numerous types withcompounds which themselves have separate sensitizing properties and theregions of spectral sensitivity of which coincide at least in part withthe respective spectrograms of the basic sensitizers. For instance, thethiocarbocyanines and the dibenzothiocarbocyanines, unsubstituted in the8- position, respond to supersensitization by the supersensitizersherein in the same manner but not to the same degree as do the8substitute`d thiocarbocyanines. The selenium containing carbocyannesmay also be used as basic sensitizers in the same manner as thethiocarbocyanines described herein, although they do not respond tosupersensitization to the same degree. I have also found thatthe2:2'dimethyl8phenyl3 :4:3 :4' dibenzothiocarbocyanine is verymarkedly super- Sensitized by both 2:2 diethyl 8 methyl 3:4:3t4dibenzothiocarbocyanine iodide and 2:2 dimethyl 8 ethyl 3:4:8' :4'dibenzothiocarbocyanine iodide, following the procedure outlined above.

Numerous variations to the above invention will doubtless occur to thoseskilled in the art and will be included in the scope of my invention asdened by the claims appended hereto, it being understood that theforegoing is merely illustrative of the manner of practicing myinvention and the results to be obtained thereby.

What I claim as my invention and desire to be secured by Letters Patentin the United States is:

l. A gelatino-silver-halide emulsion containing two sensitizers for theemulsion, one of which is a carbocyanine selected from the groupconsisting of thiocarbocyanines and selenocarbocyanines, as a basicsensitizer, and the other of which is a dibenzothiocarbocyanine, as asupersensitizer.

2. A gelatine-silver-halde emulsion containingtwo sensitizers f-or theemulsion, one of which is a thiocarbocyanine, as a basic sensitizer, andthe other of which is a dibenzothiocarbocyanine, as a. supersensitizer.

3. A gelatino-silver-halide emulsion containing two sensitizers for theemulsion, one Iof which is a selenocarbocyanine, as a basic sensitizer,and the other of which is a dibenzothiocarbocyanine, as asupersensitizer.

,4. A gelatino-silver-halide emulsion containing two sensitizers for theemulsion, one of which is a thiocarbocyanine substituted at the centralcarbon atom of the trimethenyl chain, as a basic sensitizer, and theother of which is a dibenzothiocarbocyanine, as a super-sensitizer.

5. A gelatino-silver-halide emulsion containing two sensitizers for theemulsion, one of which is 2:2' dialkyl 8 alkyl thiocarbocyanine halide,as a basic sensitizer, and the other of which is 2:2 dialkyl 8 alkyldibenzothiocarbocyanine halide, as a supersensitizer.

6. A gelatino-silver-halide emulsion containing two differentsensitizers for the emulsion, one of which is 2:2 dialkyl 8 alkyldibenzothiocarbocyanine halide, as a basic sensitizer, and the other ofwhich is 2:2 dialkyl 8 alkyl dibenzothiocarbocyanine halide, as asupersensitizer.

7. A gelatino-silver-halide emulsion containing two sensitizers for theemulsion, one of which is 2:2 dimethyl 8 ethyl thiocarbocyanine iodide,as a basic sensitizer, and the other of which is 2:2' diethyl 8 methyl3:4:3z4' dibenzothiocarbocyanine iodide, as a supersensitizer.

- ing two sensitizers for the emulsion, one of which is 2:2' dimethyl 8ethyl thiocarbocyanine iodide as a basic sensitizer, and the other ofwhich is 2:2' dimethyl 8 ethyl 3:4:3'r4 dibenzothiocarbocyanine iodide,as a supersensitizer.

11. A photographic element comprising a gelatino-silver-halide emulsioncontaining two sensitizers for the emulsion, one of which is athiocarbocyanine, as a basic sensitizer, and the other of which is adibenzothiocarbocyanine, as a supersensitizer.

12. A photographic element comprising a gelatino-silver-halide emulsioncontaining two sensitizers for the emulsion, one of which is aselenocarbocyanine, as a basic sensitizer, and the other of which is adibenzothiocarbocyanine, as a. supersensitizer.

CHARLES. E. K. MEES.

